The rapid expansion of the aquiculture of fish and shrimp has been slowed by the persistent difficulties in raising larval fish such as sea bream, sea bass, mullet, halibut and striped bass. Fish require live prey during the larval stage of development. To be acceptable to larval fish the prey must be the proper size, shape and be palatable. The live prey must also be available at an acceptable price and quality, be amenable to culture on a commercial scale and not present other problems to the fish hatchery such as contamination of the larval fish rearing tanks. The favored live prey of fish hatcheries for larval fish has included rotifers, Artemia nauplii and copopods, although other types of live prey have also been used as food. A problem with Artemia is that the nutritional composition of the Artemia is determined by the nutritional composition of the Artemia eggs before the Artemia hatches and, in turn, the nutritional composition of the Artemia laying the eggs. In addition the quality of commercially available Artemia eggs is decreasing due to increased demand. With Artemia, the nauplii are fed to the larval fish shortly after hatching and before the nauplii have the opportunity to grow.
In addition to requirements of energy and protein, marine larval fish also require highly unsaturated fatty acids (HUFA) as essential fatty acids. In the wild, marine larval fish obtain their requirements of HUFAs from copepodites and marine algae. Within the group of highly unsaturated fatty acids, larval marine fish require more docosahexaenoic acid (DHA) than eicosapentaenoic acid (EPA) as an essential fatty acid. Some species of fish may also require arachidonic acid (ARA) as an essential fatty acid. The enrichment of Artemia with HUFA has been reported using enrichment techniques with microparticle diets and emulsions rich in n-3 HUFA esters or using algal species rich in n-3 HUFAs. A problem with these microparticle diets and emulsions is the high cost of the fish oil used to enrich the microparticles with the HUFAs. Another problem is that the oil droplets have a limited capacity to load various nutrients into the droplet and are totally unsuitable for carrying water soluble nutrients such as essential amino acids.
The enrichment of Artemia nauplii using algae has many problems. One problem is that the algae can contribute to fouling of the larval rearing tanks. See C. M. Hernandez-Cruz et al. Larvi '95 Fish and Shellfish Larviculture Symposium pp 511-514, herein incorporated by reference, reporting that enriching rotifers with lipid emulsions leads to an increase in the number of bacteria associated with the rotifers which may affect the bacterial flora of the larval rearing tank.
J. O. Eujemo et al. in Larvi '95 Fish and Shellfish Larviculture Symposium pp 109-110 report that "docosahexaenoic acid (DHA), is more important than eicosapentaenoic acid (EPA) for the physiological function of marine fin fish larvae, including survival, growth and pigmentation success. However, contrary to other live feeds, the enrichment of Artemia with DHA is difficult because of the inherent catabolism of the latter fatty acid upon enrichment. These problems, as well as others, have prevented the enrichment of live feeds with DHA."